Carpet, particularly nylon carpet, is the floor covering of choice in many households and businesses. Unfortunately, carpet has a limited lifespan and must eventually be replaced, with the resultant used carpet waste generally being sent to landfill. The vast quantities of carpet waste that are generated annually are burdensome to landfill capacity and have a negative impact on the environment. Furthermore, most carpet is made with nylon as the face fiber, a material that is relatively expensive. The quantity of used carpet discarded every year amounts to a loss of billions of dollars in potentially reusable carpet components.
To reduce the impact of used carpet on the environment, and to reclaim some of the financial loss due to discarding of fibers and other useful carpet material waste, carpet recycling would appear to be a logical solution. Recycling carpet, however, is difficult because its three major components are chemically and physically diverse. Most carpet consists of about 20-50 weight percent face fiber, the remainder being backing materials, commonly polypropylene, and an adhesive which attaches the carpet fiber to the backing material. The adhesive typically comprises a carboxylated styrene-butadiene (XSB) latex copolymer, and inorganic filler like calcium carbonate. Further, while cured thermosetting systems may under certain circumstance be recoverable, they are not capable of being reused as raw polymeric components in the manufacture of a second generation carpet.
To recycle carpet, the face fibers are typically separated from the adhesive and backing to be reprocessed into new products or to be chemically recycled. Various methods for the mechanical removal of carpet fiber have been used. These methods disadvantageously result in low yield of the recycled carpet fiber. For example, U.S. Pat. No. 6,610,769 discloses a method of employing an adhesive that can be completely removed by applying shear in the presence of an aqueous alkaline solution. In another example, U.S. Pat. No. 5,240,530 discloses a method of grinding carpet to a fiber length of less than about one-quarter inch and washing in a water bath to allow the various materials of the carpet to be separated by density.
In a further example, U.S. Pat. No. 5,230,473 describes a method for disintegrating, separating, and segregating whole carpet by loosening and debonding a latex/filler binder system by repeated application of highly pressurized fluids consisting of air, water, heated air, steam, and chemical solutions, and repeated stripping with rotating elements.
In another example, U.S. Pat. No. 5,722,603 describes a method of recovering face fiber from a carpet employing numerous steps of shredding and subjecting it to impact forces to reduce particle size, screen separating and washing the particles, followed by separation in water in a hydrocyclone. The washing operation optionally includes additives to improve the wetting and separation of the particles, such as sodium hydroxide and nonionic surfactant.
Another method to recycle carpet is to dissolve the carpet fiber itself from the remaining components. For example, U.S. Pat. No. 5,840,773 describes a method of extracting nylon from carpet waste by dissolving it in an alcohol-water agent. This method disadvantageously uses large quantities of organic solvent. In a further example, U.S. Pat. No. 5,889,142 describes a method of extracting nylon from carpet waste by dissolving it in a caprolactam-water mixture. This method also requires large quantities of organic solvent.
In still a further example, U.S. Pat. No. 5,932,724 describes a method of depolymerizing multi-component waste material which is fed to a reactor as an extruded melt and contacted with superheated steam at high temperature and pressure to provide caprolactam which can be purified and polymerized. Lastly, U.S. Pat. No. 5,916,410 describes the difficulty of recycling carpet fibers and describes a process involving the use of an organic softener.
Accordingly, there is a need to provide improved methods and systems for recycling one or more component parts of carpet. Further, there is a need to provide improved carpet recycling methods and systems that can yield reclaimed materials suitable for use in the manufacture of second generation carpets. Still further, there is a need for the manufacture of carpet structures comprising one or more materials that have been reclaimed from a post consumer carpet.